The present invention relates generally to speed sensor assemblies for use in motor vehicles and, more particularly, to a speed sensor assembly having a bimetallic sensor mount for mounting a speed sensor to a support structure.
As is well known, speed sensor assemblies are used in motor vehicle applications to detect the rotational speed of a rotary member (e.g., wheels, axleshafts, propshafts, etc.). The signal generated by the sensor is typically used to control actuation of vehicle systems such as, for example, anti-lock braking systems, four-wheel drive and all-wheel drive torque transfer systems, torque biasing or limited slip axle systems and electronic stability control systems.
Most speed sensor assemblies are equipped with a sensor that is operable to detect discontinuities, such as gear teeth, along a target surface. The target surface can be formed on the rotary member or can be formed on a target member, such as a tone wheel or exciter ring, that is mounted to the rotary member. In its environment of use, the speed sensor assembly requires a sensor mount for mounting the sensor to a stationary support structure. For example, one relatively common vehicular mounting arrangement for a speed sensor assembly utilizes a Hall-effect sensor which is mounted to the axle housing and an exciter ring that is secured to the axleshaft. The sensor mount for this arrangement typically employs a steel boss that is welded to the axle housing. Once the steel boss has been welded to the axle housing, it is machined to receive the sensor, as well as fasteners employed to both orient and secure the Hall-effect sensor to the axle housing. During prolonged vehicle operation, the steel boss on the axle housing tends to oxidize. If iron oxide forms at the mounting interface between the sensor and the boss, the position of the sensor may change relative to the exciter ring. Due to the operational characteristics of the Hall-effect sensor, a change in sensor position relative to the exciter ring can result in a loss of wheel speed sensing capability. Accordingly, a need exists for providing a speed sensor assembly having a sensor mount that is resistant to corrosion.